1. Technical Field
The present invention relates to a line inkjet printer performing printing with ink discharged from each nozzle of a plurality of head modules configuring a line head and, more particularly, to a line inkjet printer having a plurality of line heads for each color.
2. Background Arts
In the field of the inkjet printer, the line inkjet printer having enabled realization of fast printing by performing so-called one-path printing in a sheet-width direction of a print sheet (main scanning direction) becomes popular. In the line inkjet printer, a line head configured by arranging a plurality of head modules side by side in the main scanning direction is used. In particular, in a line inkjet printer performing color printing with ink of a plurality of colors, a plurality of line heads for each color is provided.
The line head of each color is attached to a common head holder at intervals in a transfer direction of a print sheet (sub scanning direction) and driven at shifted timings according to the intervals. Due to this, ink droplets of each color land on the same pixel of the print sheet in an overlapping manner.
Consequently, if there exists a displacement in the attachment position with respect to the head holder in any of the head modules in the line head of each color having a nozzle corresponding to a certain pixel, the ink droplets of each color land on the corresponding pixel being displaced but not overlapped with each other. If the landing positions of the ink droplets of each color are displaced, there occurs a trouble that the color of the pixel becomes a color different from the original color. The trouble that the landing positions of the ink droplets of each color are displaced from one another in a certain pixel occurs also when there is a difference in the discharge direction characteristics of ink droplets between the head modules of each color.
In order to solve the displacement in the landing position of the ink droplets of each color, in Japanese Patent Laid-Open No. 09-239971, a so-called multipass inkjet printer is proposed, in which the head reciprocates on the carriage. In this proposal, date about the characteristics of landing position of ink droplet by the orifice plate of the head of each color incorporated in the base of the carriage is given and the discharge operation is performed using the date so that the ink droplet lands on the correct position.
However, taking similar measures in a line inkjet printer having a remarkably larger number of nozzles requires a tremendously large configuration and an enormous amount of processing, and therefore, it is impractical.
On the other hand, Japanese Patent Laid-Open No. 2006-168241A has proposed measures when there is a displacement between the discharge directions of ink droplets of two nozzles neighboring across two head modules of the same line head in a line inkjet printer. However, this proposal only prevents the occurrence of light and deep stripes on an image printed by monochrome printing and does not serve as measures against the change in color in multicolor printing.